Lithium-ion batteries have made great strides in the field of portable electronic products due to their high operating voltage, high safety, long life and absence of memory effect, among other characteristics. With the development of new energy vehicles, lithium-ion batteries have great application prospects in power supply systems for new energy vehicles.
In a lithium-ion battery using a non-aqueous electrolyte, the non-aqueous electrolyte is a key factor affecting the high- and low-temperature performances of the battery. In particular, the additive in the non-aqueous electrolyte is particularly important for effecting the high- and low-temperature performances of the battery. During the initial charging of the lithium-ion battery, lithium ions deintercalate from the cathode material of the battery, pass through the electrolyte, and embed into the carbon anode. Due to its high reactivity, the electrolyte reacts on the surface of the carbon anode to produce compounds such as Li2CO3, LiO, LiOH, etc., thereby forming a passivation film on the surface of the anode, which is termed solid electrolyte interface (SEI) film. The SEI film formed during the initial charging process not only prevents the electrolyte from further decomposing on the surface of the carbon anode, but also has a tunneling effect for lithium ions, allowing only lithium ions to pass through. Therefore, the SEI film dictates the performances of the lithium-ion battery.
In order to improve the performances of lithium-ion batteries, many researchers have attempted to enhance the quality of the SEI film by adding various anode film-forming additives (such as vinylene carbonate, fluoroethylene carbonate, vinylethylene carbonate) to the electrolyte, so as to improve the performances of the battery. For example, JP-2000-123867A proposes improving battery characteristics by adding vinylene carbonate to the electrolyte. Vinylene carbonate can have precedence over the solvent molecules in undergoing a reductive decomposition reaction on the surface of the anode to form a passivation film on the surface of the anode, which prevents the electrolyte from further decomposing on the surface of the electrode, thereby improving the cycling performance of the battery. However, the addition of vinylene carbonate results in generation of gases during storage of the battery at high temperatures, causing the battery to swell. In addition, the passivation film formed by vinylene carbonate has a high impedance, especially under low temperature conditions, such that lithium precipitation is prone to occur during charging at low temperatures, thus affecting battery safety. Fluoroethylene carbonate can also form a passivation film on the surface of the anode to improve the cycling performance of the battery, and the passivation film formed has a relatively low impedance, which can improve the low-temperature discharging performance of the battery. However, fluoroethylene carbonate produces more gases during storage of the battery at high temperatures, which significantly reduces the high-temperature storage performance of the battery. Although vinylethylene carbonate can improve the high-temperature storage performance of the battery, the passivation film formed has too high an impedance, which seriously degrades the low-temperature discharging performance of the battery, and results in serious lithium precipitation during charging at low temperatures, thus affecting battery safety. Although existing anode film-forming additives can significantly improve certain performances of the battery, it is difficult to achieve the high- and low-temperature performances at the same time.